Coded track circuit signaling system



P N-. D. PRESTON 2,357,545

CODE D TRACK CIRCUIT SIGNALING SYSTEM Filed Sept. 30, 1941 9 Sheets-Sheet 1 FI'GLLA.

INVENTOR WMW Sept. 5, 1944. N. D. PRESTON V CODED TRACK CIRCUIT SIGNALING SYSTEM Filed Sept. :50, 1941 9 Sheets-Sheet 2 Sept. 5, 1944. N. D. PRES 'I 'ON CODED TRACK CIRCUIT SIGNALING SYSTEM Filed Sept. 30, 1941 9 Sheets-Sheet 5 N. D. PRESTON 'CODED TRACK cIRcUiT SI GNALiNG SYSTEM Sept. 5, 194 4 Filed Sept. 30 1941 9 sagas-sheet! mum INVENTOR ww.

N. D. PRESTON CODE ED TRACK CIRCUIT SIGNALING SYSTEM Sept 5, 1944.

Sept; 5, 1944. N. D. PRESTON CODED TRACK CIRCUIT SIGNALING SYSTEM Filed Sept. 50, 1941 9 Sheets-Sheet 9 G a n u. H3 3 u n/ 3 m mNm E NE- For. 3% JF N NM N QQ DQ Patented Sept. 5, 1944 CODED TRACK CIRCUIT SIGNALING SYSTEM 'Neil D. Preston, Rochester, N. Y., assignor to General Railway Signal Company, Rochester, N. Y.

Application September 30, 1941, Serial No. 413,021

52 Claims.

The present invention relates to automatic signaling systems for railroads, and more particularly to the application of direct current coded track circuits to the control of Wayside signals for a single track railroad for providing protection for both opposing and following train movements substantially equivalent to a line wire absolute-permissive-block signaling system.

The conventional coded track circuit provides that impulses of current are successively applied to one end of a track circuit section with spaced intervals conveniently termed off periods to comprise a driven code, the impulses of which are applied at selected rates in accordance with trafilc conditions of an adjacent track circuit section. At the opposite end of the track circuit section, suitable code responsive means is employed to receive the driven code impulses and decode such impulses in accordance with their rate for distinctively controlling the indication of a signal governing traffic into that track circuit section without the use of any line wires.

In my prior application, Ser. No. 365,065, filed November 9, 1940, a coded track circuit is disclosed in which an inverse code is transmitted in a direction opposite to the driven code by impressing impulses upon the track circuit during the oil periods of the driven code at the end of the track circuit section which is receiving the driven code. Then suitable means is employed to receive the inverse code impulses at the end of the track'circuit section sending'the driven code. In my above-mentioned application, I disclose means for checking or insuring the integrity of the inverse codereceiving means, and the system of the present invention applies the principles of such a checked coded track circuit to an A. P. B. signaling system. However, it is to be understood that no claim is made herein to any subject matter disclosed in such above mentioned prior application. 7

In the system of the present invention, the coding apparatus for all of the track circuit sections is normally in operation and organized so that the head-block signals at any given passing siding are normally clear to permit trains to leave that passing siding in either direction.

One of the objects of the present invention is to provide that the prevailing direction of .driven code in the track circuit sections at the opposite ends of a stretch of single track shall betoward their respective head-block signals to not only provide that the head-block signals shall be normally clear, as above mentioned, but also to facilitate in the provision of double distant caution control and the overlap siding control usually provided in A. P. B. systems. The system of the present invention also contemplates that any intermediate track circuitsection in a stretch of single track shall have its normal driven, code in a predetermined prevailing direction; and that the prevailing direction of the driven code in the siding section of track shall also be for a predetermined selected direction.

Another object of the present invention is t provide novel means for reversing the prevailing direction of driven code in the track sections as required to clear signals for train movements, but at the same time to facilitate the restoration of the direction of driven code to the prevailing direction after the passage of a train in a manner to eliminate prolonged code flights.

. In an A. P. B; system, it is necessary to provide What has been conveniently termed a tumble: down circuit organization which acts when a train enters a stretch of single track to place all opposing signals of the stretch at stop. With such an arrangement, it is necessary to provide what is commonly known as a directional stick relay associated with each of the intermediate signals to so act on the tumble-down circuits as to permit following train. movements with the usual block spacing.

Thus, another object of the present invention is to provide a novel control for directional stick relays for use in coded track circuit A. P.-B. signaling systems. This novel control is of the socalled straddle-joint type, that is, a train must pass from one track section into another over the intervening insulated joints in order to pickup the directional stick relay for the corresponding direction of travel.

This is accomplished in the present invention by including in the pick-up circuit for a given directional stick relay a back contact of the decoding means for the track section in approach to a signal in addition to afront contact of a series track relay for the track section in advance of that signal with means for allowing such pickup circuit to be closed only momentarily after the train passes the signal. Such an organization assures that a train must actually be present on a track section and travelling in a direction corresponding to the direction of trafiic governed by the signal which it is passing.

Other objects, purposes, and characteristic features of the present invention will be in part obvious from the accompanying drawings and in part pointed out as the description-of the inven t on pr gresses.

In describing the invention in detail, reference will be made to the accompanying drawings in which like letter reference characters provided with distinctive numerals designate corresponding parts through out the several views, and in which;

Figs. 1A, 1B, 1C and 1D, when placed end to end, illustrate an A. P. B. signal system organized in accordance with the present invention.

Fig. 2 illustrates a diagram of the normal conditions of the system.

Figs. 3A to 3F illustrate diagrams of the different conditions of the system for east-bound train movements.

Figs. 4A to 4F illustrate diagrams of the different conditions of the system for west-bound train movements.

Figs. 5A to SF illustrate diagrams of the different conditions of the system for east-bound following train movements.

Figs. 6A to 6F illustrate diagrams of the different conditions of the system for west-bound following train movements.

Figs. 7A to 7F illustrate diagrams of the different conditions of the system. for two opposing train movements for a meet at a passing siding.

For the purpose of simplifying the illustration and facilitating in the explanation, the various parts and circuits constituting the embodiment of the invention have been shown diagrammatically and certain conventional illustrations have been employed, the drawings having been made more with the purpose of making it easy to understand the 1principles and mode of operation than with the idea of illustrating the specific construction and arrangement of parts that would be employed in practice. Thus, the various relays and their contacts are illustrated in a conventional manner, and symbols are used to indicate connections to the terminals of batteries, or other sources of electric current, instead of showing all of the wiring connections to these terminals.

The symbols plus and minus are employed to indicate the positive and negative terminals respectively of suitable batteries or other suitable sources of direct current; and the circuits with which these symbols are used always have current flowing in the same direction.

Referring to Figs. 1A, 1B, 1C and 1D when placed end to end, it will be seen that a stretch of single track is shown extending between the head-blocks of two passing sidings with the apparatus at such head-blocks so organized that the positioning of duplicates of Figs. 1A, 1B, 1C and 1D to the right of Fig. 1D (or to the left of Fig. 1A, as the case may be) illustrates the circuit organization required forthe control past the siding as contemplated in accordance with the present invention. This has been illustrated in the traffic movement diagrams of Figs. 2, 3, 4, 5, 6 and 7. It will thus be seen that by reproducing the figures of the present disclosure and selecting their relative positions to each other, the signaling system required for the various track layouts afforded by a single track railroad will be completely disclosed.

Referring to Figs. 1A, 1B, 1C and ID a stretch of single track between two passing sidings of a single track railroad has been illustrated. This stretch of single track has signals 1 to 8, inclusive, for governing traffic thereover in opposite directions, and for the purposes of the present disclosure they have been shown to be of the color-light type with suitable marker lamps to indicate the absolute or stop-and-stay signals when the marker is in vertical alignment with the main signal, but to indicate a permissive or stop-and-proceed signal when the marker lamp is oiT-set from the main signal. Although color-light type signals have been illustrated, it is to be understood that many other types, such as search-light signals, position light signals, and the like, might well be employed, the color-light type of signal being selected as a convenient means for illustrating the different signal indications given under the various conditions of traflic.

With reference to Fig. 2, which illustrates diagrammatically the normal conditions of the system, it will be seen that the portion of the railway shown in Figs. 1A to 1D inclusive has been assumed to be re-produced and placed to the right of Fig. 1D so as to illustrate a stretch of single track between passing sidings A and B, and another stretch of single track between passing sidings B and C.

In these diagrammatic illustrations of the condition of the system under varying trafiic movements, symbols have been used to indicate the controlled conditions of the various signals, and the signal arms of such symbols have been shown heavy for those signals which are. illuminated. In other words, the usual symbol with the light line semaphore arm indicates the controlled condition of a signal without the illumination of its lamps; while the symbol having the heavy line signal arm indicates not only the controlled condition of the signal but also that its lamps are illuminated.

It is noted that the even numbered signals are for governing east-bound traflic, while the odd numbered signals are for governing westbound traffic (see Figs. 1A, 1B, 1C and 1D). Also, the track section between any two opposing signals has been given a reference character corresponding to those signals, as for example, the section of track between signals 2 and 3 has been designated track section 23T, so as to readily identify the various adjoining track sections which are, of course, suitably insulated from one another.

Each signal location has its associated apparatus which is quite similar to the apparatus associated with every other signal with a few exceptions. These similar devices have been given the same letter reference characters which are made distinctive by reason of the preceding numerals which correspond with the number of the signal with which they are associated. Thus, the apparatus may be described in general with reference to such apparatus by the letter reference characters instead of specifying the particular signal location with which such device is associated.

It is assumed that the coded track circuit is of the conventional direct current type, using primary batteries, or trickle-charge storage batteries as a source for the track circuit current, but it should be understood that the same principles may be applied to coded track circuits energized from alternating current sources.

It is also contemplated that the transmitted driven codes are of specified distinctive rates, such as '75, and on and off periods per minute, although any other suitable rates might be employed. These different rate codes are produced from suitable code generating devices such as code oscillators in accordance with cause the immediate picking up of the series re the usual practice, the contacts of such osillators being illustrated. diagrammatially as C15, C120. or Cl8fl,, as the case may be. For the |purpose of this disclosure, the code oscillator contacts. Cl5,Cl20,- and CEBU are .assumed to be on separate oscillators for the difierent rates, all

of which are normally operating at their respec-. tive rates; and each. signal location is provided with oscillators individual to that location as required for the different codes transmitted from that location. It is to beunderstood that such oscillators may have starting and stopping means employed so as to cause their operation only when any particular oscillator is required 'to supply a code. It is also to beunderstood that various kinds of code generators or oscillators may be employed, and that a single motor might drive coding contacts for all three difierent ratesif desired.

' For the purpose of illustrating the codes employed under varying trafiic conditions, an' arrow' with a solid line shaft is used to designate the direction and presence of a driven code, while anarrow with a dotted line shaft is used to indicate the presence and direction of an inverse code. Also, the numbers 75, 120- or 180 appearing closely adjacent these arrows indicate the rate of the code represented by such arrow. The arrows of Figs. 1A, 1B, IC'and 1]) show the codes normally appearing in the various track sections with theprevailing directions, of course, indicated. The same conditions are also illustrated in Fig. 2 where the two stretches of single track have been shown, thus giving a more complete picture of the signaling conditions associated with the opposite ends of a passing siding.

In the track circuit "sections at the opposite ends of a stretch of single track adjacent the head-block signals, the prevailing direction of the driven code is toward the head-block signals and the direction of the inverse code must, therefore, be away from the head-block signals. In the intermediate track circuit sections, such as section 4.-5T, the direction of driven code under normal conditions could be in either direction but for convenience in the illustration the prevailing direction has been shown as being from right to left. The same thing is true with regard to the siding track circuit section 8IT where the normal prevailing direction of driven code could be predetermined for either direction but for the purpose of the disclosure has been assumed to be from right to left.

The various codes are supplied to the track circuits by code transmitting relays CP which are two-position polar type relays. The contacts of each of these code transmitting relays CP are normally biased to one position to connect the associated track relay TR across the track rails and are effective when in the opposite or operated position to connect the associated battery in series with the associated series'track relay SR across the track rails. The track relays TR are also of the two-position polar type having their contacts biased to a particular position, while the series track relays SR are of the neutral type with suitable operating margins to allow the usual coding current to be applied to the track circuit without picking up. However, when a train is present in the associated track circuit section and the series relay SR with its associated battery is connected across the track rails. the series relay SR then picks up. Although the track circuits might be organized so'that the entranceof a train into any given track circuit section would lay SE: at the; distant end of that section, it is contemplatedinaccordancewith this invention that the series-relay will not pick up until the train is pproximately half way through a track circuit, section. This arrangement assures a more positive action of the series relay, especially on the drop away when a train leaves the section. 7

Each track relay TR has associated therewith a neutral track repeating relay T? which is energized upon each energization of its associated track relay TR. It should also be noted in this connection, that the trackrelays TR respond both to theadrivenf codes and to the inverse codes, the distinction between the different codes being made in the control circuits. i

The code transmitting group of apparatus'also includes a code sending relay CS 'atcertain locations, such as the head-block signal locations and those intermediate signal locations which are at the receiving end of the normal driven code of an intermediate track circuit section.

One of the significant features characteristic of this invention is that the control circuits for the code transmitter relays CP include back-contacts oftheir respective track relays TR. Thus, any given code sending relay CP cannot be ener-. gized to transmit the nextv impulse of a driven code until its associated track relay TR has been released after responding to the impulse of an inverse code. This checks the reliability of the reception of an off or inverse code as will be explained more in detail hereinafter.

Associated with each signal location that must transmit an off code or an inverse code is an off code transformer TF which is energized upon each energizationof its associated track relay TR and is deenergized when such associated track relay'is released. The energization of the transformer TB, of course,'induces a current in its. secondary winding which flows through the 3550-. ciated transmitter relay C]? over the inverse code controlling circuit, but this current flow is of such a direction as to fail to actuate the contacts ofthe polar relay GP to operated positions. On the other hand, the current induced in the secondary of this off code transformer TF when the associated track relay TR-is deenergized, is of a proper direction and intensity to momentarily actuate the associated code sending relay CP. In this way, an off code or inverse code pulse is momentarily placed upon the track rails be-, tween any two successive impulses of a driven code, such inverse code of course being applied only under the proper trafiic conditions as will be explained later. However, it should be pointed out that this method of providing an inverse code may be varied so as to use battery energy through suitable circuit control means without the inductive transformer arrangement and still be with-, inthe scope of the present invention.

The decoding apparatus at each signal location includes two decoding transformers TFA and TFB; a home relay H; and distant relay D. The home relays H are of the neutral type and are connected to the first decoding transformer TFA in such away as to be responsive to any code received over the track rails above a' given rate, that is, each home relay H responds to all of the 3 code rates '75, 120. and 180. These home relays H are designed so as to remain picked up when receiving. pulses for even the slow 75 code rate, but to drop away immediately upon the cessation of any of the codes. The distant relay D is con,- nected through a rectifier arrangement, a transformer TFB, and a condenser to the first trans-- former TFA in such a way as to form a resonated circuit combination responsive only to the 180 code rate. At certain signal locations, such as at signal 8 of Fig. ID, a distant relay DX is connected through a transformer TFC and rectifier arrangement so as to be responsive only to the 120 code rate.

Certain of the home relays H have associated therewith slow-acting repeater relays HP which directly repeat the picked up and dropped away condition of their respective home relays H with predetermined time intervals of delay.

Each signal, except the signals governing traffic into a siding section, has an associated directional stick relay S which is picked up by the passage of a train past that signal in the direction which it governs.

It is believed that further characteristics of the system will be best understood by considering its operation for certain typical traflic conditions.

OPERATION GeneraL-It is believed expedient before considering in detail the circuit organization, to briefly outline the mode of operation of the system as to the codes employed for the communi cation of signal control conditions through the various track circuit sections with more particular consideration of the direction of code transmission under certain traffic conditions. Such traffic conditions and codes are illustrated in the diagrams of Figs. 2 through 7 to which reference will be made as the description progresses.

With reference to Fig. 2, the normal conditions of the system are illustrated in which the control apparatus for each of the signals is conditioned for the clear indication of such signal, although only the leaving signals, such, for example, as signals 2 and I, actually display clear indications, while the other signals are normally dark. In other words, all of the signals are approach lightbe cleared by a driven code.

ed except the leaving or head-block signals which are continuously illuminated.

A 180 driven code is normally transmitted through each of the track sections. The direction of driven code transmission for each siding section is normally from right to left,'while the direction of driven code transmission for each of the end sections of each stretch of single track between sidings is normally toward the adjacent siding. The prevailing direction of driven code transmission for the intermediate track sections of each stretch of single track between sidings has been shown to correspond with that for the siding sections for the sake of uniformity, but it should be understood that the opposite direction of prevailing driven code may be selected for either section. It will also be noted from Fig. 2 that the driven code of each track section has an associated inverse code transmitted in a direction opposite to the normal direction of such driven code.

Although it appears from Fig. 2, that signals are controlled to clear condition by inverse codes, the system is so organized that a train proceeds for usual train movements in accordanc with signals cleared by driven codes. When a train approaches a track section in which the normal direction of driven code corresponds with the direction of the train, means is provided to automatically reverse the direction of the driven code from its normal direction so that it will be transmitted toward the train to clear the signal at the entrance to such section.

This feature will be better understood by reference to Fig. 33, where the train of Fi 3A has moved into the track section 2-3T, which causes the direction of driven code to be reversed in the track section 6--lT so as to cause the signal 6 to Incidentally, the entrance of the train into the track section 23T causses the approach lighting of both the signals 4 and It is desirable to clear signals for usual train movements by driven codes, because there are a greater number of distinctive driven codes than there are inverse codes available for controlling any given signal in accordance with the various traffic conditions. .1 7

As mentioned above, the prevailing direction of the driven codes in the end track sections of each stretch of single track i toward th adjacent siding, which facilitates the provision of single block sidin over-lap control for the signals governing entrance to the siding track sections. This feature of over-lap control will be discussed later in connection with the diagrams of Fig. '7.

Fig. 3A is the first in a series of figures illustrating the condtions of the system upon passage of an eastbound train when the trackway is assumed to be unoccupied for a considerable dis: tance in advance of such train. The presence of the east-bound train in the siding section 8IT of siding. A, as illustrated in Fig. 3A, is effective to cause a restrictive indication to be displayed by the opposing signal 2, but signal 3 is not caused to display a caution indication unless an opposing train is in approach to signal 3 to cause the reversal in the direciton of driven code transmission in the end track section 23T adjacent the Siding A. Conditions involving opposing trains will be hereinafter discussed,

Considering the progress of the east-bound train as illustrated in Fig. 3B, the entrance of the train into the stretch of track between the sidings [A and B causes the dropping away of the H relays for the signals 3 and 5 by removing the inverse code which is normally transmitted for their energization. The dropping away of such relays of course causes the signals 3 and 5 to be conditioned for the display of stop indications, but such indications are not displayed because the approach lighting is not effective under these conditions. The removal of the inverse code transmitted from left to right throughtrack section 4-5T for the control of signal 5 causes the driven code transmitter for the left-hand end of the track section 6-'IT to become inactive for the transmission of adriven code, and such inactivity is effective to cause the reversal in the direction of driven code transmission in the track section B--'IT. With the reversal in the direction of driven code transmission in that track section 6-1T, the code transmitter at the left-hand end thereof becomes active for the transmission of an inverse code from left to right through such such track section, but the reception of such inverse code at the right-hand end of the track section cannot be effective to clear the signal 1 although it does cause the relay H for that end of the track section to be energized. The signal 1 is held at stop under such conditions because of the energized condition of the relay 'ICS for that end of the track section 6-1T, which relay 'ICS is picked up upon the shiftin in the direction of driven code transmission through the track sec.- tion. It is by this mode of operation that train detection is effective for the track section 6--1T for east-bound trains whil at .the same time maintaining the entering signal I at stop in accordance with the general principles of absolutepermissive-block signaling systems.

The putting to stop of signal I cancels the inverse code transmitted from left to right through the siding track section 8IT of siding B, and conditions the apparatus at the righthand endof the siding B so that the signal I is controlled to stop, although the signal is main tained dark. Thiscondition, however, would not exist if there were a west-bound train in approach to the signal I on track section 2-3'1, as the approach of such train would cause the reversal in the direction of driven code transmission through the sidin section 8IT, and the reversal of the direction of code transmission in that section would cause the signal I to be put tocaution if the overlap section 6'IT were unoccupied by the east-bound train a illustrated in Fig. 3B. The mode of operation under conditions whereopposing trains are involved will be more readily understood hereinafter when reference is made to the conditions illustrated in Figs. 7A through 7F.

When the siding track section for the siding A becomes unoccupied in th rear of the eastbound train, the conditions of driven and inverse code transmission arerestored except that a 120 driven code is transmitted rather than a 180.code

as selected by the east stick relay for signal 2.

The 120 code causes the conditioning of the entering signal at the opposite end of the siding to indicate caution, but such signal is dark unless it is being approachedlby atrain. The 120 code in the siding sectionof courseprovides'that the D relay for the control of signal I cannot be picked up, and therefore such signal is put to caution. The caution indication of signal I provides for a back up move of the east-bound train. The conditions are different for the control of signal Ifor a backup move from the control of such signal fora usual west-bound train movement as willv be apparent as th descriptionprogresses.

As the east-bound train proceeds further along the trackWay-as illustrated inFig. so as to occupy the track section 4-5T, it will be noted that the advance of the train to such track section has no material affect .upon the conditions of code transmission in advance of'the train. When the track section 2-.3T in the rear ofthe train becomes unoccupied, the normal direction of driven code transmission is restored for that track section, and the signal 2 for governing entrance to that block is properly put to caution in accordance with the '75 driven code transmitted through such track section. This condition of code transmission isof course selected in accordance with the picking up of the east stick relay for the signal4.

The advance of an'east-bound train into the track section, 6-'IT as illustrated in Fig. 3D does not alter the conditions of code transmission for the track sections in advance of thetrain if no opposing train is present. ''However, it will be dered inactive if an opposing train is .immediately in appro ch o e e in gn I 91 condition is illustrated in Fig. 7D. When the track section 4-5T becomes unoccupied in the rear of the east-bound train, restoration becomes .efiective similar to that described for the track. section 2-.3T when it became'unoccupied by the train, -a -75 driven code being transmitted irorn right to left through the trachsection 45T .for ov ning he ca t n n cati n o i n i The picking up of the 4H relay at the left-hand end of track section 4-5T undersueh conditions changes the code transmitted frornright to left .throughthe track section 2 3T to complete the -restoration to normal of the conditions of code transmission 'for such -tracl section. Th transmission of an inverse code from left .to right through the track section 45T under the conditions illustrated in Fig. 3D causes the signal 5 .to be put to caution in accordance with the 75 .code transmitted through that track section.

T i .of u se. i rdance-With hed h- .e s zed c n i n .o h e ayiD o sushsieha When t as ound nadvan esflht h siding section 8IT ofsiding B, asillustrated in Fig. 3E, it will be noted that the normal condi- :tions f, .code a smiss ;for he track sec ion in adva ce o t e. tra n ar maint ined- Whe th t ac ect fil' "b omes un u ied h therear of the train, there is a temporary code fight between the driven code transmitters jor ditions depending upon the reception of the inverse code at theright-handend of the adjacent track section.4 5T. The reception of the driven code at the right-hand end -of-track -s ection '6-'IT.causes the clearing of signal Land causes the transmission of an inverse code fro m right to left through the-track section in; accordancewith the normal conditions as-illustrated in Fig. 2. The receptionof' thex-i l erse-code at the left-hand end of track sectionfi-ITeauses the 75 driven code formerly transmitted-through the track section 4-5T to be changed to a 180 driven code, and thusto complete the restoration to normal-of the conditions for the-stretch of single track between the siding -A and B.

The advance of the east-bound train from the siding'section 8IT for the siding Binto the track section 2-3T, as illustrated in Fig-3F, causes conditions to be established in advance and in the rear of the train corresponding to those which have been consideredwith reference to a similar trafiicconditionillustrated ,inFig.

313. It will be noted upon comparing Figs. 3E

and SF with specific reference to the. direction of driven code transmission in the siding section 8IT, that a code fight occurs between the transmitters for the opposite ends of such track section when it becomes unoccupied by a train.

-However, the apparatus of the system. is -so;.or-

ganized as to cause the direction of drivemcode 7 transmission to be established from;-right to left in accordance with the predetermined prevailing direction of the driven code.

After having considered the'general mode A of oper t n th temupompassa fifanie stb un rain. th o a p cal rtiqmoftrackv -in approach to such signal.

way, it will be readily apparent with reference to Figs. 4A through 4F that the mode of operation upon the passage of a west-bound train is somewhat similar, although it is necessarily modified to some extent because of the necessity for reversing the direction of driven code transmission upon the approach of a West-bound train to a siding section, such as track section 8IT, and upon the approach of a west-bound train to an intermediate track section such, for example, as the track section 45T.

With reference to Fig. 4A, when a west-bound train enters the stretch of track between the sidings B and C, the direction of driven code transmission is reversed for the end track section 23T by a mode of operation similar to that which has been described under similar circumstances for the entrance of an east-bound train into a stretch of single track between sidings. The condition is different for the intermediate track section 4--5T, however, in that the driven code normally transmitted from right to left through such track section is removed when the tumble-down becomes effective for such stretch of track, and the removal of such code track section in the rear of the west-bound train in Fig. 4A are restored to norm-a1 in a manner generally similar to that described in connection with Fig. 3B for the restoration to normal of the codes transmitted for an east-bound train. The putting to stop of the opposing entering signal 2 upon the tumble-down when the west-bound train enters the stretch of single track between sidings B and C, causes the code in the siding sections 8--IT for the siding B to be changed from a 180 code to a '75 code. Such change is, of course, effective to cause the relay 8D for the left-hand end of the siding B track section to be dropped away, and thus condition the control apparatus for signal 8 so that such signal would display caution upon the approach of an eastbound train.

th conditions 'of Fig. 3F, the code transmitted is a 120 code, and under the conditions of Fig.

' 4A, the code transmitted is a 75 code. The reception at the left-hand end of the track section 8-IT of the 120 code causes the energization of a relay 8DX by a tuned circuit, and the energization of such relay is effective to cause the intermediate signal 6 in the rear of the entering signal 8 to be cleared if there is a west-bound train However, if a westbound train is in approach to the signal 6 when a 75 driven code is transmitted through the siding section 8|T, the signal 6.is put to caution because of the transmission of a 75 code through the track section 6'IT as selected by the deenergized condition of the relay 8DX for the lefthand end of the siding section 8IT. Although such conditions are not particularly obvious from the diagrams which have been considered, they are more readily apparent under traffic conditions involving opposing train movements shown in Figs. 7A'through 7F and discussed in detail hereinafter. But it is believed suflicient at this point in the description to understand that by this mode of operation, a single caution indication is provided for following trains, and a dou ble caution indication is provided for opposing trains in accordance with the desired practice in absolute-permissive-block signaling systems.

The advance of the west-bound train into the track section 4-5T so as to cause the track section 6'IT to become unoccupied in the rear of the train as illustrated in Fig. 4B allows the restoration of driven and inverse code transmission through the section 6'IT in a manner very similar to that heretofore described when considering the passage of an east-bound train as illustrated in Fig. 30.

When the intermediate track section '4-5T becomes unoccupied in the rear of the westbound train, a code fight is effective for such track section as illustrated by the arrows representing the direction of driven code transmission in Fig. 4C, and the code transmitter for the right-hand end of the track section is effective to over-rule th transmitter at the opposite end to establish the normal direction of driven code transmission. The conditions illustrated in Fig. 4C for track section 45T are therefore only momentary, as the solving of the code fight is effective to establish the conditions for the track section 45T as illustrated in Fig. 4D. The reception of the driven code at the left-hand end of the track section 45T causes the transmission of an inverse code to the right to give clear conditions to the apparatus for signal 5, but the lamps of signal 5 remain dark. On the other hand, if a following west-bound train were to approach signal 5, the driven code and the inverse code shown would be cut off by such following train while the energization of the westbound stick relay for signal 3 would be effective to cause a '75 driven code to be transmitted from left to right to control signal 5 to display a caution indication as will be described in connection with Fig. 6A.

The advance of the west-bound train into the section 8IT associated with the siding B as illustrated in Fig. 4E causes restoration to become effective for the track. sections in the rear of the train in the manner similar to the mode of operation which has been described when considering the passage of an east-bound train.

When the siding section 8IT becomes unoccupied in the rear of the east-bound train as illustrated in Fig. 4F, the solving of a cod fight for the transmitters for the opposite ends of that track section in favor of the driven code transmitter for the right-hand end of the track section allows restoration to the normal conditions of the system for code transmission through that track section. Although the apparatus for the control of signal I is conditioned for the clearing of such signal in accordance with the normal conditions of the system, the reversal in the direction of driven code transmission through the siding section 8|T upon the approach of signal I by a following West-bound train would be effective in accordance with the energized condition of the west-bound stick relay for signal 1 to cause a 75 driven code to be transmitted from left to right for the caution indication of signal I. This condition is illustrated in Fig. 6D.

. Having thus described the general mode of operation of the system upon the passage of respectiv'e east and west-bound trains, it is believed that the mode of operation for other traffic conditions, as illustrated in Figs. 5, 6 and '7, will be readily understood as the description progresses.

Normal conditions With reference to Figs. 1A, 1B, 1C and 1D placed end-to-end in that order, it will be noted that the system is normally in operation so that the apparatus at each of the signal locations is in operation to normally produc codes as indicated by the arrows shown in Fig. 2 adjacent the track. Thus, the decoding relays H and D associated with the various signal locations are normally energized in accordance with the normallytransmitted codes so as to normally clear the signals, all of which has been explained in general in connection with the conditions described with respect to the diagram of Fig. 2.

Inasmuch as the apparatus at each of the various signal locations is similar in its organization, and the interconnecting track circuits are also similar, it is believed that the detailed consideration of the operation of the apparatus associated with one particularly track circuit section will be sufficient for an understanding of the operation of the apparatus associated with the other track circuit sections. There are, of course,.certain exceptions to this general similarity, as for example, the control of the code transmitter relays CP, which control will be discussed in detail with respect to each of such relays.

As a specific example of the normal conditions of code communication through a track section, the conditions will be described in detail relative to the end track section 23T (see Figs. 1A and 1B). The code transmitter relay 3GP (see Fig. 1B) is normally active for the transmission of a 180 driven code because of its energization for each impulse of the oscillator Cl8il. The circuit by which relay 3GP is energized for each impulse of oscillator C180 extends from including contact 29 of relay 3TB, in its left-hand position, contact 2| of oscillator ,Cl80, front contact 22 of relay 4H; and winding of relay 3GP, to

During each pulse of relay 3GP the contact 23 is actuated to its left-hand position, and in that :position it closes the track circuit for track section 2?-3T for the transmission of a driven code impulse. The track circuit is closed under such conditions from the positive terminal of track battery 24 including contact 23 of relay 30? in .its left-hand position, lower rail of track section 2 3T, contact 25 of relay 2CP (see Fig. 1A) in its left-hand position, winding of relay ZTR, upper rail of track section 23T, and winding of the series relay 3SR (see Fig. IE), to the nega- -tiVe terminal of track battery 24. The energi- ..zation of that track circuit for each pulse of the code transmitter relay 3GP is effective to cause the contact of relay 2TB, to be actuated to its right-hand position, but the series relay 3SR of course does not respond, as the characteristics of such relay are marginal in that the series relay is active only when the track section is shunted by a train relatively close to the signal 'locationwith which such series relay is associated.

For each pulse of the track relay 2TB, (see Fig. l A), the relay 2TP is picked up by the energization of an obvious circuit closed at contact 26 of relay 2TB. in its left-hand position. The picking upfof the relay T1? for each pulse received closes an obvious circuit at front contact 7 6 21 for the upper portion of the rimary winding of transformer ZTFA. The closing of back contact 2! of relay 2TP at the end of each impulse ofthe code received closes a circuit for the lower portion of the primary winding of transformer 2TFA to cause a reversal in the direction of energization as compared to the energization of the upper portion of the Winding in accordance with the closure of front contact 27.

In accordance with the'reversal in the direction of energization of the primary winding of the transformer ZTFA responsive to the pulsing of contact 2'! of relay 2TP, the relay 2H is normally maintained energized by the alternating current set up in the secondary winding 28 of transformer ETFA as rectified by the contact 29 of relay ZTP. That is, the shifting of contact 21 of relay 2TP in synchronism with contact 29 causes the secondary winding 28 of transformer 2TFA to'have its upper and lower portions alternately connected to the relay 2H so as to cause such relay to be energized by pulsating direct c r t, v.

An' alternating current is al o set up in the secondary winding 30 of transformer ZTFA when a code is being received at the left-hand end of track section 2-3'1, and the alternating current thus setup flows through a tuned circuit including the primary winding 3| of transformer 2TFB. The secondary winding 32 of the transformer Z 'IFB is connected across a full-wave rectifier 33 which provides for the feeding of direct current to the relay 2D in an obvious manner. The tuned circuit for the primary Winding of the transformer ZTFB is tuned so as to cause sufficient current to fiovv for the picking up Of the relay 2D only when a 180 code is being received at that end of the track section 23T.

Each H relay has a repeater relay HP which is normally energized. For example, the relay ZHP is normally energized by an obvious circuit closed at front contact 34. The circuit for the control of relay 2HP is typical of the circuit provided for the control of each of the other relays HP.

In accordance with the energized condition of the relays 2H and 2D, the leaving signal 2 for the siding B normally displays a clear indication because of the energization of thegreen lamp of .such signal by a circuit closed from including back contact 35 of relay ZCS, front contact 36 of relay 2H, front contact 3! of relay 2D, and the green lamp G of signal 2, to

The transformer 2TF has its primary winding energized for each impulse received at the lefthand end of track section 23T by the energization of an obvious circuit closed at contact 38 of relay 2TB, in its left-hand position. Upon the opening of such contact at the end of each impulse. received under normal conditions, the collapse of the flux in the transformer 2TF causes an induced voltage in the secondary winding of the transformer to be effective to pick up the code transmitter relay 2GP for the transmission of an impulse of an inverse code. The relay 2GP is energized under such conditions by a circuit extending from the left-hand terminal of the secondary winding of the transformer 2TF including front contact 39 of relay 2H, back contact 40 of relay 2G8, and winding of relay 2GP, to The relay 2GP is of course only mo mentarily picked -up as its energization is terminated when the collapse of the flux of the transformer 2TB has become complete. Due to :the polar characteristics of the relay 2CP, it is not responsive to the flow of current through its winding upon the building up of the flux in the transformer 2TF.

The picking up of the relay for the transmission of an impulse of an inverse code causes the picking up of the track relay 3TB. (see Fig. 1B) at the right-hand end of the track section 23T by the energization of a circuit extending from the positive terminal of track battery 4| (see Fig. 1A) including contact of relay 2CP in its right-hand position, lower rail of track section 23T, contact 23 of relay 3GP (see Fig. 1B) in its right-hand position, winding of relay 3TR, upper rail of track section 23T, and winding of the series relay ZSR (see Fig. 1A) to the negative terminal of track battery 4|.

At the right-hand end of track section 2-3T, the relay 3T]? (see Fig. 1B) follows the inverse code received in accordance with the pulsing of contact 42 of relay 3TB, and the pulsing of contacts 43 and 44 of relay 3TP causes the relays 3H and 3D to be picked up by the energization of circuits which correspond with those that have been specifically described for the energization of the relays 2H and 2D for the left-hand end of the track section. the relays 3H and 3D is not effective, however, to cause the signal 3 to display a clear indication, as the circuits for the lamps of such signal are open at back contact 45 of relay 4H1.

The code transmitter relay ICP (see Fig. 1A) for the right-hand end of the track section 8IT is normally active for the transmission of a 180 driven code from right to left through that track section because of the energization for each impulse of the oscillator C|80 of a circuit is effective to cause the transmission of a driven code by the energization of a track circuit similar to that described for the track section 23T except that such track circuit does not include a series relay SR. To consider the manner in which the driven code transmitted from the right-hand end of the siding section 8|T for the siding B is received at the left-hand end of the track section, Fig. 1D should be placed to the left of Fig. 1A. With the figures arranged in this manner, it will be noted that the reception of the 180 driven code causes the pulsing of contact 52 of relay 8'I'R. (see Fig. 1D), and the pulsing of such contact causes the pulsing of relay 8TP. The pulsing of contact 53 of relay 8TP at a 180 rate causes the relays 8H and 8D to be normally energized in a manner corresponding to that described for the energization of the relays 2H and 2D, but the energization of such relays cannot be effective for causing the illumination of the green lamp of signal 8, because the circuit for such lamp is open at back contact 54 of relay 'IHP.

Each time contact 55 of relay 8TB in its lefthand position is opened at the end of an impulse, the relay 8GP is picked up for the transmission of an inverse code impulse by the energization of a circuit extending from the left-hand terminal of the secondary winding of transformer SFT including front contact 55 of'relay ll-I, back contact 51 of relay 'ICS, front contact 58 of relay 8H, and winding relay 8GP, to The reception of the 180 inverse code at the right-hand The energized condition of pulse of the oscillator CI80.

end of track section 8l T causes the pulsing of contact 46 of relay ITR (see Fig. 1A), and the track repeater relay ITP of course follows the pulsing of that contact. The pulsing ofv contact 59 of relay ITP causes the picking up of relays IH and ID by the energization of circuits corresponding to those described for the energization of relays 2H and 2D except that the circuit for relay IH includes normally closed contact 60 of the switch circuit controller for the track switch IW. The energized condition of relays IH and ID does not cause the illumination of the green lamp of signal I under normal conditions as the circuit for such lamp is normally open at back contact 6| of relay 2H1.

A 180 driven code is normally transmitted from right to left through the track section 45T by the relay 5GP (see Fig. 1C) in accordance with the energization of such relay for each im- The circuit for relay 5CP under such conditions extends from including contact 62 of relay 5'IR in its left-hand position, contact 63 of oscillator Cl80, front contact 64 of relay 6H, and winding of relay 5GP, to The pulsing of contact 65 of relay 5CP causes the transmission under normal conditions of a 180 driven code from right to left through the track section 45T by the energization of a track circuit corresponding to that which has been described for the track section 2-3T, such track circuit differing from the track circuit for track section 2--3T only in the inclusion of normally closed contact 66 of the track switch 2W which normally closes a circuit around the insulated joint 61. a

The pulsing of contact 68 of relay 4TB (see Fig. 1B) upon the reception of the 180 driven code causes the relay 4TP to follow the code, and the pulsing of contact 69 of relay 4TP causes the relays 4H and 4D to be normally energized by the energization of circuits corresponding to those described for the energization of the relays 2H and 2D, respectively. The signal 4 is normally dark because of the open condition of back contact ll] of relay 3I-IP.

Each time the contact 1| of relay 4TB in its right-hand position is open, the relay 4CP is picked up for the transmission of an inverse code impulse from right to left through the track section 45T by the energization of a circuit extending from the left-hand terminal of the secondary winding of the transformer 4TF including front contact 12 of relay 3H, back contact 13 of relay 40S, and Winding of relay 4GP, to

The reception at the right-hand end of the track section 45T of the inverse code causes the pulsing of contact 62 of relay 5TR (see Fig. 1C), and the pulsing of such contact causes the relay 5TP to follow the code. The pulsing of contact 14 of relay 5'I'P causes the relays 5H and 5D to be normally picked up by the energization of circuits corresponding to those which have been described for the relays 2H and 2D, respectively. The signal 5 is normally dark because of its circuit being open at back contact 15 of relay GHP.

Inaccordance with the energized condition of the relay 5H, the code transmitter relay BCP is normally active to transmit a 180 driven code from left to right through the track section 6- IT. The relay BCP is energized for each impulse of the oscillator Cl by the energization of a circuit extending from including contact 16 of relay 6TB in its right-hand position, contact ll of oscillator CI80, front contact 18 of relay'j5I-I, and winding of relay 6GP, to The pulsing of contact 19' of relay 6GP at a 180 rate causes the transmission of a 180 driven code throughtrack circuitof track section 61T by thee'nergization of a track circuit corresponding to' the track circuit described for the track section 2-3T.

At the right-hand end of the track section 6 4T (Fig.v 1D placed to the right of Fig. 1C). thepulsing of contact 80 of realy 'ITR (see Fig.

1D) causes the relay FTP to follow the 180 code,

and. the pulsing of contact 8| of relay 'ITP causes the picking up of the relays 1H and ID by the energization ofcircuits corresponding tothose which have been described for the relays 2H and 2D, respectively. The energized condition of the relays 1H and 1D causes the green lamp ofsignal 1 to be illuminated under normal conditions in accordance with the energization of a circuit extending from including back contact 82 of relay 'iCS, front contact 83 of relay II-I, front contact 84 of relay 1D, and the green lamp G of sigrlal'l, to

The conditions relative to the control of signal 8, and relative to code transmission and reception at the left-hand end of the track section 8IT for the left-hand end of the siding C of course correspond to the conditions which have been described when Fig. ID was considered to be placed at the left-hand end of Fig. 1A.

Posswge of east-bound train- In order that the mode of operation of the system" may be thoroughly described for a typical siding section and a typical stretch of single track between sidings, all of the conditions will be described which affect the siding section 8-l T for the siding B, and the sections of the stretch ofsingle track between the sidings B and C.

Therefore, to consider the conditions relative to the passageof an east-bound train through the siding'section 8iT, the Fig. 1D should be considered as-being placed to the left of Fig. 1A so thatthe combination of the two figures discloses a complete siding section together with the signals and control apparatus for each end thereof. Upon considering the Figs. 1D and 1A in this relationship, the manner in-which codes are transmitted through the track section 6-1T will not be considered, as it is believed that such condi: tions will be more readily understood as the description progresses when Fig. ID will be assumed to be placed at the right of Fig. 10 in .or-'

relay 'IHP, and thedropping away of such-relay, renders the illumination of the green lamp effecder; that the Figs. 1A through 1D respectively may completely disclose the circuits associated with the stretch of single track between the sidings B and C, s

It will be noted with reference to Fig. 3A that the presence of the train in the siding section 8IT for the sidingA does not alTect the normal conditions for the siding section 8|T for the siding B, but the entrance of the east-bound train into the stretch of single track between the sidings A and Baas illustrated in Fig. 33 causes the removal of the inverse code transmitted opposingsignals in the stretch of single track'betweenthe sidings B and C.

Although: the inverse code transmitted' from' left to right through the track section 6-'|T maintains the'relay 'll-I' (see Fig. 1D) picked up, the signal 1 is put to stop because of the picking up ofthe relay 'ICS which closes an obvious circuit for the red lamp of that signal at front contact 82, the opening of back contact 82 being effective to' open thecircuit which has been described for the green lamp of signal I. The conditions under which the relay 'ICS are picked up will behereinafter considered when considering in detail the A.'P,'B. tumble-down.

The picking up of the relay 'ICS is also effective to render. the'code transmit'ter 8GP inactive forthe transmission. of a code-by-the opening of back contact '51. The removal of the inverse code from the track section 8 4T for the siding B causes. the droppingaway of relays lI-Iand ID (see Fig. 1A) but the dropping-awayof these re lays has no'apparent function if the trackway is unoccupied for some-distance in advance of the east-bound train as is assumed under the conditions being described. Y The code transmitter 2C P for the left-hand end of track-section 2-3T is unaifectedbythe-droppingaway of the relays H and D, asthe circuit by whichsuch relay' is normally active for the transmission ofadriven code does not include contacts of those relays.

As the east-bound train advances so as to 00"- cupy the track section (i -1T, the shunting of that track section causes the dropping away of the. relays 1D and 'l l-l lsee Fig. -1D) at the righthand end of the track section'," but assuming there .to be no trainsin advance of theeastbound train, thedropping away of those-relays does not afiect the .conditionsof code transmission through thesiding section 8- lT. The conditions under which the dropping awayof the relays II-I and JD due to the presence of an eastbound .train in the track-section-B--'IT aredependent upon the presence'ofanother train in advance and .theywill be-hereinafter considered.

'Ihe approach: of the east-bound train to'the signal 8; in causing the droppingaway of the re- I lay ill-I, causes. the dropping away of its "repeater tive for signal Bby the energization' of a circuit extending from including'backcontact 54 of relay 'IHP, front contact 85-of relay 8H, front contact 86 of-relay 8D,and the green lamp of signa18,to'(): I

When .the east-bound train enters the siding section 8 -lT'forthe siding B as illustrated in Fig. 3E,the relays. 8H and 8D are dropped away because of the shunting of the track section by the'train; .The' shifting of contact 85 of relay 8H causes the extinguishingof the green lamp of signal '8, and causes the illumination of the red lamp of such signal by the energization ofa circuitextending from including back contact 54 of relay II-1P, back contact 85 of relay 8H, and the red lamp R. of signal 8, to It will benoted with referenceto'FigfiE that the normal conditions are restored for the track section 61T in the rear of the train, and the green lamp of signal 1 is illuminated. These conditions will be assumed to be efiective for the present" as a similar condition for theright-hand end section of the stretch of singletrack between the sidings B and'C Will behereinafter described;

The presence. of the east-bound train in the track section 8-|T of .thesiding B cannot or course aife'ct the 'drivencode transmitted toward the train, suchcode is still being transmitted, and

in addition a 180driven code is being transmitted from the left-hand end of the track section so as to follow the train. The codetransmitter for the left-hand end of thetrack section 8lT is rendered active in accordance with the dropping away of the relay 8H for that end of the track section, and in accordance with the restoration to normal conditions for the track section 6'IT. The relay 8GP is therefore active for the transmission of a 180 driven code'by the energizationv APB tumble-down To consider further progress of the east-bound train along the trackway, it will be assumed that a train accepts the clear signal! and enters the track section 23T. Upon the shunting of such track section the relays 2H and 2D (see Fig. 1A)

are dropped away, and the opening of front contact '36 of relay 2H causes the extinguishing of the greenlamp of the signal 2. The red lamp of signal 2 is illuminated upon the energization of a circuit extending from including back contact of relay ZCS, back contact 36 of relay 2H, and the red lamp R of signal 2, to H The dropping away of the relay 2H opens the circuit by which the reIay'ZCP has been active for the transmission of an inverse code at front contact 39, and the opening of front contact 34 of relay 2H causes the deenergization of the slow release repeater relay 'ZI-IP. Prior to the dropping away of the relay ZHP and subsequent to the dropping away of relay 2H a circuit is closed.

by which the series relay 25B is picked up due to the presence of the train in the track section 2-3T. The relay 2GP is momentarily energized under such conditions to close a circuit for the series relay ZSR by'a circuit closed from including back contact 34 of relay 2H, front contact 90 of relay 2H1, back contact 39 of relay 2H, back contact 40 of relay 2CS,'and winding of relay 2GP, to The relay 28R. is momentarily picked up by' an impulse caused by the picking up of relay 2GP upon the energization of a circuit extending from the positive terminal of the track battery 4|, including contact 25 of relay ZCP in its right-hand position, lower rail of closes a pick-up circuit for the stick relay 2S extending from including back contact of relay 2H, front contacts 90 and ISO of relay ZHP, back contact 19! of relay ZCS, front contact 9| of relay ZSR, and Winding of ,relay 2S, to A stick circuit is closed for relay 28 when such relay is picked up, extending from including back contact 34 of relay 2H, front contact 92 of relay 2S, and winding of relay 28, to The dropping away of the relay 2HP after the relay 2S has had time to pick up, causes the code transmitter relay 2GP to be dropped away by opening its circuit at front contact 90, and the opening of that front contact 90 and contact I90 of relay ZI-IP also opens the pick-up circuit which has been described for the stick relay 2S.

When the relay ZCP for the left-hand end of the track section '2--3T becomes inac ivefor the transmission of an inverse code, the relays 3TH. and 3 TP (see Fig. 1B) for the right-hand end of that track section become inactive, and the relays 3H, BHP and 3D are dropped away. The dropping away of such relays of course condi-' tions the signal 3 for a stop indication, but such signal is maintained normally dark as it is not being approached by a train.

The dropping away of relay 3HP causes the energization of an obvious circuit for the green lamp G of signal 4, the relays 4H and 4D being picked up at that time.

Inasmuch as the code transmitter relay 401 for the left-hand end of track section 45T is normally active for the transmission of an inverse code in accordance with the energized condition of the relay 31-1, the opening of front contact 93 of relay 3H causes the relay 4GP to become inactive for the transmission of an inverse code from left to right through the track section.

In accordance with the removal of the inverse code from the track section 4-5T, the relays 5TH and 51? (see Fig. 10) at the right-hand end of the track section become inactive and the relays 5H, 5H and 5D are dropped away.

The relay 6GP becomes inactive for the transmission of a driven code upon the opening of the circuit by which it has been normally active at front contact 1,8 of relay SE. The relay 6GP by ceasing to be active removes the driven code formerly transmitted from left to right through the track section 61T (Fig. 1D placed at the right of Fig. 1C), and the removal of such code causes the relays 'I'IR and 'ITP (see Fig. 1D) for the right hand end of the track section to become inactive, and thus cause the dropping away of the relays ll-I, 'lI-IP and ID. v

The dropping away of relay 1H closes a circuit to cause the picking up of the code sending relay TCS extending from including contact of relay 1TH, in its left-hand position, back contact 94 of relay 1H, winding of relay ICS, and back contact 95 of relay is, to The picking up of the relay ICS closes a stick circuit at front contact 96 for shunting back contact 94 of relay 1H out of the circuit just described. Such stick circuit provides the relay ICS will be maintained the reception of an inverse code.

Upon the picking up of the code sending relay 10s, a circuit is closed by which the code transmitter TCP becomes active for the transmission of a driven code from right to left through the track section 61T extending from including contact 8i! of relay ITR in its left-hand position, front contact 91 of relay 8H, front contact 98 of relay 8D, contact 99 of oscillator CIBO, front contact I00 of relay K38, and winding of relay 1GP, to

The pulsing of contact lUl of relay 1C? for the transmission of a driven code from right to left through the track'section 6'IT under such conditions causes the relays BTR. (see Fig. 1C) and BTP for the left-hand end of the track section to be active, and thus to cause the picking up of the relays 6H, BHP and 6D. In accordance with the picking up of the relays SH and 6D with the relay SHP deenergized, a circuit is closed for the energization of the green lamp of signal 6, extending from including back contact I02 of relay BHP, front contact I03 of relay 6H, front contact I04 of relay 6D, and green lamp G of signal 6, to

Conditions are established by the picking up of the relay 61-! whereby the code transmitter relay 6GP for the left-hand end of track section 6--'|T becomes energized each time relay 6TB is deenergized. Relay GCP is energized under such conditions by a circuit extending from the 1 left-hand terminal of the secondary winding of transformer BTF including back contact 105 of relay 5HP, front contact I06 of relay 6H, back contact I01 of relay 58, back contact 18 of relay be active and thus to cause the picking up of the relays 1H, lHP and 1D. The picking up of the relays II-I and 1D cannot be elfective for causing the clearing of signal I, as the circuits for the green and yellow lamps of such signal can be closed only upon the closureof back contact 82 of relay TCS which is picked up at this time. The red'lamp of signal 1 is illuminated when the code sending relay lCS is picked up by the energization of an obvious circuit closed at front contact 82.

This operation of the track relay 'ITR by inverse code pulses and the energization of the home relay !H is used to detect the occupancy of the end track section 6-'!T by an eastbound train for siding overlap control as discussed more fully later. Although the energization of this track relay 'ITR, intermittently opens its back contact 80 in the stick circuit for the code sending relay LCS, this relay 'ICS is provided with a supplemental stick circuit controlled by the operation of the coding contacts. C186 or C at the proper times and in sucha manner as to maintain this relay JCS energized while the track.relay l'IR is operated. by inverse code pulses. For this purpose the coding contacts CIBU and C15 governing the operation of the transmitter relay ICP are provided with what may be termed back contacts which are closed when the ordinary contacts of the coding device are closed for the energization of-transmitter' Considering the operation of this organization for the control of thecode sending relay 'ICS, the driven code pulses are applied when the transmitter, relay .ICP is energized :by movement of the contact finger of the coding contacts' Clfifi to the left in engagement with contact 99; and

since the inverse code pulses operate the track relaylTB. during the off intervals between the successive driven code pulses, said contact finger will be inth e right-hand. position supplying en-i ergyin multiple with the back contact 80 of the track relay 1TB, .to hold up the-relay lCS by the supplemental stick circuit during the time interval this back contact 88 is opened by an inverse code pulse. In other words, there are in effect two stick circuits for the code sending-reIayICS; one including a back contact 80 of the track relay 'ITR, and the other including the back contact of the coding contact CIBU or C15 then in effect;

' relay 2S,back contact-49 of relay for the 1 track switch and since the energization' of the track relay (TR by inverse code pulses occurs alternately and in synchronism with the operation of the coding contacts, these two stick circuits are closed alternately and in overlapping relation to maintain the codesending relay, lCS energized.

Although the conditions under which the code sending relay 70s is released are considered later, it may be pointed out here that any enerigization of the track relay ITR at a time other than during the regular off period for the driven code in effect, such as wouldbe caused by'an opposing and overlapping driven code pulse, will automatically release the relay 'ICS by holding 7 :open the back contact of the track relay 'ITR at the time when the coding contacts CIBU or C'l5'operate for the next driven code pulse. In this connection, it should be noted that operation of the coding contacts C I80 or C15 for the ;next driven code pulse is not effective to energize this contact 80.- Consequently, any energization of the track relay 'ITR prolonged beyond the off interval of the driven code, as by an opposing driven code pulse, is efiective for its full duration independently of the operation of thecoding contacts CIBU or C15.

The samecircuit organization and mode of operation just described forthe code sending relay .708 also applies to the code sending relay, ZCS for the other end of the single track stretch.

The circuit by which the code transmitter relay BCP is normally active for the transmission of an inversecode from ,left to right through the track section 8-.lT is opened at back contact 5?) of relay TCS' upon the picking up of that relay, and thereforethe inverse code normally transmitt-ed from left to rightthrough the track section 8--IT is removed. The removal of the inverse code causes the H and D relays for the right-hand end of the track section to be dropped away in a manner and for purposes corresponding to those which have been described under corresponding traffic conditions where it was assumed that an eastbound train had entered the stretch of single track between sidings A and B as illustrated in Fig. 3B.

Passage of east-bound train through stretch between sidings I -When the progress of the east-bound train" is occupied in the rear of the train, there is a code fight between the driven code transmitters forthe opposite ends of such track section, and the arrangement of the circuits is such thatthe transmitter for the right-hand end of the track section over-rules the transmitter for the lefthand end thereof. At the right-hand end of' the track section the energized condition of the stick relay 28 (see 1A) with the. relay 2H?- dropped away is effective to cause the code transmitter relay lCP for the'right-hand end of track section 8-!T to be picked up for each impulse of the oscillator CIZG by the energization acircuit extending from including contact. 46 of relay I'IR in its left-hand'position, con-- tact Hi8 of oscillator C120, front contact Hi5 of v ZI-IP, normally closed contact 50 of the switch circuitcontroller; IW; and winding of relay 

